The present invention is directed generally to catalyst systems for polymerizing olefins. More specifically, the present invention provides novel cocatalysts or activators suitable for activating metallocene catalysts for olefin polymerization, supported catalyst systems including the novel catalysts and metallocene catalysts, and methods of polymerizing olefins using the supported catalyst systems.
Activation of metallocene complexes for olefin polymerization requires the use of a cocatalyst or activator. Only a limited number of such cocatalysts are known. One type of cocatalyst includes dialkylaluminum chlorides and trialkylaluminum compounds. Dialkylaluminum chlorides work well only with titanocenes (Natta, J., Pino, P., Mazzanti, G. and Giannini, U., J. Am. Chem. Soc. 79, 2975 (1957), and Breslow, D.S. and Newburg, N.R., J. Am. Chem. Soc. 79, 5072 (1957)). Some trialkylaluminum compounds are known to activate zirconocenes, but are very poor cocatalysts for metallocene complexes (U.S. Pat. No. 2,924,593). Another type of cocatalyst includes alkylalumoxanes. These cocatalysts are described in Andersen et al., Angew. Chem., Int. Ed. Engl. 15, 630 (1976); Sinn, H. and Kaminsky, W., Adv. Organomet. Chem. 18, 99 (1980); and Sinn, H., Kaminsky, W., Vollmer, H.J. and Woldt, R., Angew. Chem., Int. Ed. Engl. 19, 390 (1980). A combination of trimethylaluminum and dimethylaluminum fluoride is also known (Zambelli, A., Longo, P., and Grassi, A., Macromolecules 22, 2186 (1989)). Additional cocatalysts include compounds or salts which generate non-coordinative anions such as [R3NH]+[B(C6F5)4]xe2x88x92; see, Ewen, J.A. et al., Makromol. Chem. Macromol. Symp. 4849, 253 (1991); Taube, R. and Krukowka, L., J. Organomet. Chem. 347, C9 (1988); Bochman, M. and Jaggar, A.J., J. Organomet. Chem. 424, C5-C7 (1992); and Herfert, N. and Fink, G., Makromol Chem. Rapid Commun. 14, 91-96 (1993).
Certain zirconium complexes containing pi-bonded organic ligands, such as bis(cyclopentadienyl)zirconium complexes, activated with an alumoxane, are particularly effective catalysts; see, e.g., U.S. Pat. Nos. 4,542,199 and 4,404,344. However, although such zirconium-based catalysts are very effective olefin polymerization catalysts, the alumoxane cocatalysts are expensive and can be utilized efficiently only if the olefin polymerization reaction can be carried out in aromatic solvents (generally in toluene).
Thus, there is a need in the art for cocatalysts capable of efficiently activating metallocene complexes, particularly zirconium, titanium and hafnium complexes. In addition, there is a need for alternative, less expensive cocatalysts effective for activating metallocene complexes.
The present invention provides a new type of cocatalyst which is capable of activating metallocene complexes in olefin polymerization reactions. The cocatalyst of the present invention in general includes: (a) a halo-organoaluminum compound of the formula:
AlnRmX3n-m
where Al is aluminum, each R is independently a C1 to C4 alkyl group, X is a halide, n is 1 or 2, and m is determined by the valency of Al; and (b) a dialkylmagnesium compound of the formula:
MgRxe2x80x22 
where Mg is magnesium and Rxe2x80x2 is a C2 to C6 alkyl group. The components (a) and (b) are used in amounts such that the molar ratio of Al:Mg is at least 2, preferably from 2:1 to 5:1.
Cocatalysts of the present invention can be used in combination with metallocene catalysts to form active metallocene catalyst systems, preferably supported metallocene catalyst systems. Thus, the present invention also provides novel supported metallocene catalyst systems including a cocatalystactivator as described above, a metallocene catalyst, and a support. In the case of zirconocene complexes, each component, if used alone, does not produce an olefin polymerization catalyst, but when the components are used together, they readily activate metallocene complexes for polymerization reactions. The present invention is further directed to methods of polymerizing olefins, particularly ethylene or ethylene and an alpha olefin comonomer, using the supported metallocene catalyst systems.